1. Field of the Invention
The present invention relates to methods of opening obstructed biological conduits. Preferred methods of the invention include methods and systems for opening obstructed biological conduits using local delivery of a therapeutic agent, particularly a protease, to lyse the extracellular matrix of the obstructing tissue.
2. Background
Obstructions to biological conduits frequently result from trauma to the conduit which can result from transplant, graft or other surgical procedures wherein the extracellular matrix of the obstructing tissue largely comprises collagen. Balloon angioplasty is a common initial treatment for stenosis or stricture obstruction that yields excellent initial results (Pauletto, Clinical Science, (1994) 87:467–79). However, this dilation method does not remove the obstructing tissue.
It only stretches open the lumen, the trauma of which has been associated with the release of several potent cytokines and growth factors that can cause an injury which induces another round of cell proliferation, cell migration toward the lumen and synthesis of more extracellular matrix. Consequently, balloon angioplasty is associated with restenosis in nearly all patients (Pauletto, Clinical Science, (1994) 87:467–79). There is currently no treatment that can sustain patency over the long term.
The extracellular matrix, which holds a tissue together, is composed primarily of collagen, the major fibrous component of animal extracellular connective tissue (Krane, J. Investigative Dermatology (1982) 79:83s–86s; Shingleton, Biochem. Cell Biol., (1996) 74:759–75). The collagen molecule has a base unit of three strands, of repeating amino acids coiled into a triple helix. These triple helix coils are then woven into a right-handed cable. As the collagen matures, cross-links form between the chains and the collagen becomes progressively more insoluble and resistant to lysis. When properly formed, collagen has a greater tensile strength than steel. Not surprisingly, when the body builds new tissue collagen provides the extracellular structural framework such that the deposition of hard collagen in the lesion can result in duct obstruction.
Benign biliary stricture results in obstruction of the flow of bile from the liver and can result in jaundice and hepatic dysfunction. If untreated, biliary obstruction can result in hepatic failure and death. Billary strictures can form after duct injury during cholecystectomy. They can also form at biliary anastomoses after liver transplantation and other biliary reconstructive surgeries (Vitale, Am. J. Surgery (1996) 171:553–7; Lilliemoe, Annals of Surgery (1997) 225).
Historically, benign biliary stricture has been treated surgically by removing the diseased duct segment and reconnecting the duct end-to-end, or connecting the duct to the bowel via a hepaticojejunostomy loop (Lilliemoe, Annals of Surgery (1997) 225). These long and difficult surgeries have significant morbidity and mortality due to bleeding, infection, biliary leak, and recurrent biliary obstruction at the anastomosis. Post-operative recovery takes weeks to months. More recently, minimally invasive treatments such as percutaneous balloon dilation have been utilized, yielding good initial biliary patency results (Vitale, Am. J. Surgery (1996) 171:553–7; Lilliemoe, Annals of Surgery (1997) 2250). However, balloon dilation causes a localized injury, inducing a healing response that often results in restenosis (Pauletto, Clinical Science, (1994) 87:467–79). Long-term stenting at the common bile duct with flexible biliary drainage catheters is another minimally invasive alternative to surgery (Vitale, Am. J. Surgery (1996) 171:553–7). However, these indwelling biliary drainage catheters often become infected, or clogged with is debris, and must be changed frequently. At present, long-term treatment of biliary stricture remains a difficult clinical problem.
Patients with chronic, end-stage renal failure may require replacement of their kidney function in order to survive. In the United States, long-term hemodialysis is the most common treatment method for end stage chronic renal failure in the U.S. In 1993, more than 130,000 patients underwent long term hemodialysis (Gaylord, J. Vascular and Interventional Radiology (1993) 4:103–7); more than 80% of these patients implement hemodialysis through the use of a synthetic arteriovenous graft (Windus, Am. J. Kidney Diseases (1993) 21:457–71). In a majority of these patients, the graft consists of a 6 mm Gore-Tex tube that is surgically implanted between an artery and a vein, usually in the forearm or upper arm. This high flow conduit can then be accessed with needles for hemodialysis sessions.
Nearly all hemodialysis grafts fail, usually within two years, and a new graft must be created surgically to maintain hemodialysis. These patients face repeated interruption of hemodialysis, and multiple hospitalizations for radiological and surgical procedures. Since each surgical graft revision consumes more available vein, eventually they are at risk for mortality from lack of sites for hemodialysis access. One estimate placed the cost of graft placement, hemodialysis, treatment of complications, placement of venous catheters, hospitalization costs, and time away from work at as much as $500 million, in 1990 alone (Windus, Am. J. Kidney Diseases (1993) 21:457–71).
The most frequent cause of hemodialysis graft failure is thrombosis, which is often due to development of a stenosis in the vein just downstream from the graft-vein anastomosis (Safa, Radiology (1996) 199:653–7. Histologic analysis of the stenosis reveals a firm, pale, relatively homogeneous lesion interposed between the intimal and medial layers of the vein which thickens the vessel wall and narrows the lumen (Swedberg, Circulation (1989) 80:1726–36). This lesion, which has been given the name intimal hyperplasia is composed of vascular smooth muscle cells surrounded by an extensive extracellular collagen matrix (Swedberg, Circulation (1989) 80:1726–36; Trerotola, J. Vascular and Interventional Radiology (1995) 6:387–96). Balloon angioplasty is the most common initial treatment for stenosis of hemodialysis grafts and yields excellent initial patency results (Safa, Radiology (1996) 199:653–7). However, this purely mechanical method of stretching open the stenosis causes an injury which induces another round of cell proliferation, cell migration toward the lumen and synthesis of more extracellular matrix. Consequently, balloon angioplasty is associated with restenosis in nearly all patients (Safa, Radiology (1996) 199:653–7). There is currently no treatment which can sustain the patency of synthetic arteriovenous hemodialysis grafts over the long term.
Intimal hyperplasia research has focused largely on the cellular component of the lesion. The use of radiation and pharmaceutical agents to inhibit cell proliferation and migration are active areas of research (Hirai, ACTA Radiologica (1996) 37:229–33; Reimers, J. Invasive Cardiology (1998) 10:323–31; Choi, J. Vascular Surgery (1994) 19:125–34). To date, the results of these studies have been equivocal, and none of these new treatments has gained wide clinical acceptance. This matrix is composed predominantly of collagen and previous work in animals has demonstrated that systemic inhibition of collagen synthesis decreases the production of intimal hyperplasia (Choi, Archives of Surgery (1995) 130:257–261).
During normal tissue growth and remodeling, existing collagen matrices must be removed or modified. This collagen remodeling is carried out by macrophages and fibroblasts, two cell types which secrete a distinct class of proteases called “collagenases” (Swedberg, Circulation (1989) 80:1726–36; Trerotola, J. Vascular and Interventional Radiology (1995) 6:387–96; Hirai, ACTA Radiologica (1996) 37:229–33). These collagenases rapidly degrade insoluble collagen fibrils to small, soluble peptide fragments, which are carried away from the site by the flow of blood and lymph.
See also U.S. Pat. Nos. 5,981,568; 5,409,926; and 6,074,659.
It thus would be desirable to provide new methods to relieve obstructions blocking flow through biological conduits.